1. Field of the Invention
This invention relates to an ion implantation apparatus and more particularly to an ion implantation apparatus suitable for use in the production of semiconductors or semiconductor material.
2. Description of the Prior Art
In the ion implantation apparatus used for the production of semiconductors, ions of a predetermined mass number dispersed by a magnetic field are focused on a slit and passed through the slit to be directed toward a target.
The target is rotated about an axis which is parallel to a passage through which the ions travel, with the rotation radius being equal to a distance between the passage and the axis. The target is also moved in the radial direction at a speed which is inversely proportional to the radius in order to make uniform the ion implantation on the target.
In general, a control mechanism for the movement of the target at a speed inversely proportion to the radius is undesirably complicated. Therefore, a substitutive expedient for the radial movement of the target has been proposed wherein the ions are electrostatically scanned in the radial direction.
In the electrostatic scanning type arrangement, electrons coexisting with the ions are attracted by electrostatic force, with the result that mutual repulsion of ions scatters ions in all the directions, raising a different problem that efficiency of the ion implantation on the target is lowered. This problem is aggravated in the case of implantation of a large ion current.